1. Field of the Invention:
The present invention relates to a resistive material, a resistive paste which can be fired in a neutral or reducing atmosphere, and a resistor to be formed by the use of the resistive paste.
2. Description of the Related Art
In general, a ceramic substrate comprising alumina, zirconia or the like has circuit patterns for electrodes, resistors, etc., in order that various electronic parts can be mounted thereon. Electrodes (electrode patterns) are generally formed on the substrate by screen-printing a noble metal paste comprising silver, a silver-palladium alloy or the like followed by firing the thus-printed paste in air.
However, since a noble metal paste such as that mentioned above is not only expensive but also problematic in its migration resistance, the tendency for such an expensive noble metal paste to be replaced by a base metal paste comprising, as the conductive component, copper, nickel, aluminum or the like has become accepted in this technical field. Such a base metal paste can be screen-printed on a substrate and then fired in a neutral or reducing atmosphere to give an inexpensive and good electrode pattern.
In this case, it is desirable that the resistive paste which is to form resistors (resistor patterns) on the substrate, by which the plural base electrodes as formed by firing the printed base metal paste are connected with each other, can also be fired in a neutral or reducing atmosphere.
Therefore, various resistive pastes that can be fired in a neutral or reducing atmosphere to form resistors (resistor patterns) have heretofore been proposed. Such resistive pastes includes, for example, resistive pastes comprising LaB6 such as those described in Japanese Patent Publication Nos. 59-6481 and 58-21402, resistive pastes comprising NbB2 such as those described in Japanese Patent Laid-Open No. 63-224301, resistive pastes comprising solid solutions of NbxLa1xe2x88x92xB6xe2x88x924x such as those described in Japanese Patent Laid-Open No. 2-249203, etc.
However, conventional resistive pastes such as those mentioned above are problematic in that, when they are desired to have a resistance value that is variable within a broad range by varying the mixing ratio of the resistive material consisting the paste to glass frit to be added thereto, even a slight variation in the amount of the glass frit in the paste often results in a rapid variation in the resistance value of the paste (that is, the resistance value of the paste greatly depends on the composition of the paste) and therefore the reproducibility of the desired resistance value of the paste is poor. Therefore, such conventional resistive pastes are still problematic in that they can be formed into practicable resistors having a resistance value only within a narrow range between 10 xcexa9/square and 10 Kxcexa9/square.
Apart from the above, other resistive pastes comprising a resistive material of RuO2, SrRuO3, CaRuO3 or the like have also been proposed. However, resistive pastes comprising RuO2 are problematic in that, when they are fired in a neutral or reducing atmosphere, RuO2 is reduced to Ru metal with the result that they cannot be formed into resistors. Resistive pastes comprising SrRuO3 or CaRuO3 are also problematic in that, if the proportion of glass frit to be therein is increased more than a certain degree, the resistance value of the pastes suddenly becomes too great and therefore the reproducibility of the desired resistance value of the pastes is extremely poor.
The present invention seeks to solve the above-mentioned problems in the prior art and to provide a resistive paste which can be fired in a neutral or reducing atmosphere to surely give resistors having any desired resistance values within a broad range including values of even greater than 10 Kxcexa9, a resistive material which constitutes the resistive paste, and a resistor which can be formed by the use of the resistive paste and which can realize resistance values within a broad range while the reproducibility of the realizable resistance values is good.
The resistive material which the present invention provides so as to attain the above-mentioned object is characterized in that it has a composition of a general formula:
CaxSr1xe2x88x92xRuO3
wherein x is from 0.25 to 0.75 moles.
The resistive paste which the present invention also provides so as to attain the above-mentioned object is characterized in that it comprises a solid component consisting of from 5 to 65% by weight of the resistive material and from 35 to 95% by weight of a non-reducible glass frit and an organic vehicle.
The resistor which the present invention also provides so as to attain the above-mentioned object is characterized in that it is formed by coating the resistive paste on a substrate and then firing it thereon.